AGGLUTINATION PLATE HAVING CONCAVE WELLS

Abstract: A plate (10) for use in agglutination assays having a plurality of concave-shaped wells (18) interpersed among a planar surface (12). Surrounding the planar surface (12) is a trough (14) which serves to collect samples which may have spilled out of the wells (18). The concave-shaped wells (18) are provided with opaque and low glare or matte finishes which improve the skilled and unskilled reader's ability to distinguish degrees of agglutination assay response. The diameter and depth ratio of the wells (18) characterizes the dimensions of the wells (18) which best provide distinction of agglutination responses.

Description: AGGLUTINATION PLATE HAVING CONCAVE WELLS This invention relates to agglutination assays and plates or slides upon which such assays are conducted. More particularly, this invention relates to a plate for conducting agglutination assays in which the visual distinctions in agglutination responses are optimized. In an agglutination assay, solid particles, such as, for example, latex particles, are sensitized with a binder which may be an antigen or antibody specific for an analyte. The particles are contacted with a sample suspected of containing the analyte. The presence of analyte is evidenced by agglutination of the solid particles. Many agglutinations, particularly latex agglutinations, for various diagnostic and similar purposes have been performed in microtiter plates or on planar glass, cardboard, or other such materials where the planar characteristics do not provide for containment of the reagents in their reaction mixture and the depth and dimensions of the microtiter plates render reading of the results of agglutination assays difficult if not impossible even under the best of circumstances. t Particularly under circumstances where done in laboratory settings of bright high intensity lighting, or in . home or field use where light is of irregular intensity, there has been, for this additional reason, a need to improve the type of devices suitable for making optimum qualitative and quantitative readings of agglutination assays visually rather than by means requiring expensive and delicate instrumentation subject to the surrounding conditions. In accordance with the present invention, the inventors have discovered that the use of shallow but comparatively wider concave shaped wells in opaque and low glare or matte finished devices improve the skilled and unskilled reader's ability to distinguish degrees of agglutination assay response. Thus in one aspect of the invention, there is provided a multi-well plate for visualization in an agglutination assay where the wells are characterized or shaped so as to optimize the visual inspection of distinctions in agglutination response. In a preferred embodiment, the diameter to depth ratio characterizes the dimensions of the well that best provide distinction of agglutination response. Also, the well may include a concave wall which has a bottom portion. In one embodiment, the plate has a plurality of wells, each of which has a diameter of from about 3/8 inch to about 1 inch, preferably at about 11/16 inch, and a depth of from about 3/32 inch to about 7/32 inch, preferably from about 3/32 inch to about 1/8 inch. Such plate, in general, has a diameter to depth ratio of from about 1.5:1 to about 11:1, preferably from about 5:1 to about 8:1, more preferably from about 7:1 to about 7.5:1. The plate may be formed from a wide variety of materials known to those skilled in the art. Materials from which the plate may be formed include, but are not limited to, thermoplastics such as polystyrene and copolymers thereof; polyethylene and copolymers thereof; polypropylene and copolymers thereof; polybutylene and copolymers thereof; halopolymers such as polyvinyl chloride; polyvinylidine flouride; ethylene/chlorotrifluoroethylene copolymers; hexafluoroisobutylene/vinylidene fluoride copolymers; polytetrafluoroethylene; chlorotrifluoroethylene/ ethylene/vinylidene fluoride terpolymers; and ethylene/tetrafluoroethylene/hexafluoroisobutylene terpolymers. It is to be understood, however that the scope of the present invention is not limited to any particular material from which the plate is formed. In one embodiment, the agglutination assay plate having the concave wells is made of a high impact polymeric material, particularly polystyrene and copolymers of polystyrene which can be mixed with pigments prior to thermosetting for formation of the finished three dimensional configuration of the plate. Such pigments are intended to be of a hue or color that contrasts distinctly with the color produced by the reaction of the reagents in the agglutination mixture so as to simplify visual distinction of fine differences in the reaction of the reagents. For example, a white matte background of the well and the remainder of the plate is suitable in those agglutination assays which use darker colors as end product reaction coloring or high intensity colors as end reaction visual results. In contrast, where lighter, i.e. white or pastel color reaction mixture results are expected, one would use a concave well plate having a matte finish and a black or other dark opaque pigment formed in the thermoset of the polymer material. In another embodiment, the concave well agglutination plate has a planar surface into which the concave wells are set and which planar surface is surrounded by a trough formed in the surface or plate of the polymer material. One of the disadvantages that has been observed in previous thermoset or thermoformed polymeric plates or wells, ( eg., microtiter plates,or other reaction devices) has been that they tend to deform as they cool and become unstable on a planar surface. Formation of the trough in the three-dimensional configuration of the overall device of the invention provides dimensional stability during this cooling and setting period such that the finished device when ready for use is stable on the surface where it is to be used to perform assays. Further, this trough may have a depth that is as great or greater than the depth of the concave wells so that the base of the trough forms a footing that surrounds the surface area in which the reaction wells are formed. In addition, when the plate is made of a thermoplastic material such as those hereinabove described, the plate may be cut into "strips" if only a small number of wells is required for a particular assay. In such case, the trough also provides a footing for such "strips" of assay wells. In yet another embodiment, beyond the periphery of the above-described trough is provided a flange which extends distally from the periphery of the trough elevated from the level of the base of the trough. Thus, the flange provides further dimensional stability and provides a means for manual manipulation such as lifting and moving of the trough before, during, or after reaction in the concave wells that was previously difficult at best and often resulted in disruption of the agglutination assay or in the appearance of the resultant agglutination reaction. The plate can be employed in conducting any agglutination assay or agglutination inhibition assay known to those skilled in the art. The binder which is used in the assay in accordance with the present invention is dependent upon the analyte being assayed. For example, if the analyte is an antigen, the binder may be an antibody or a naturally occurring substance which is specific for the analyte. If the analyte is an antibody, the binder may be an antibody, an antigen, or a naturally occurring substance which is specific for the analyte. If an agglutination inhibition assay is employed, a hapten may be employed as an analyte or a binder. The assay may be employed for determining a wide variety of analytes. Examples of analytes which may be assayed in accordance with the present invention include drugs, hormones, macromolecules, antibodies, microorganisms, toxins, polypeptides, proteins, polysaccharides, nucleic acids, etc. The selection of a suitable analyte is within the scope of those skilled in the art. Analytes which may be detected in the assay include, but are not limited to. Rubella antigens. Human Immunodeficiency Virus (HIV) antigens; mononucleosis antigens and antibodies, such as mononucleosis heterophile antibodies; Streptococcus antigens, such as Group A Streptococcus antigens; toxins of C.difficile; human chorionic gonadotropin; Chlamydia antigens; digoxin; horse spleen ferritin; thyroxine (T4); insulin; triiodothyronine; follicle-stimulating hormone; lutenizing hormone; thyroid- stimulating hormone; estriol; bradykinin; prostaglandins; tumor-specific antigens; vitamins such as biotin. Vitamin B 12 , folic acid, Vitamin E, Vitamin A, and ascorbic acid (Vitamin C); metabolites such as 3' ,5'-adenosine monophosphate and 3' ,5 -guanosine monophosphate; aminoglycoside antibiotics such as gentamicin, amikacin, and sisomicin; drugs of abuse such as opium and ergot derivatives; microsomal antibody; hepatitis antigens and antibodies; allergens; and specific binding receptors such as thyroxine binding globulin, avidin, intrinsic factor, and transcobalamin. It is to be understood, however, that the scope of the present invention is not to be limited to the detection of any specific analyte. Once the latex beads are contacted with a sample suspected of containing analyte, the plate is then rotated with a standard rotator or shaker for rotating agglutination slides. Such rotation provides for collisions among the latex particles, thereby providing for agglutination of the particles if analyte is present. Due to the configuration of the wells in the plate, the plate can be rotated at speeds and for periods of time which are less than that normally employed for other agglutination assay slides or plates. In addition, before the plate of the present invention is rotated, stirring of the beads and sample in each well is not required in order to effect optimum agglutination of the latex particles, as is the case with other agglutination slides and plates. A positive result is indicated by a donut- shaped ring of agglutinated particles in the well. The invention will now be described with respect to the drawings, wherein: Figure 1 is a top view of an embodiment of the plate in accordance with the present invention; Figure 2 is a cross-sectional view along lines 2-2 of Figure 1; and Figure 3 is a cross-sectional view of the plate along lines 3-3 of Figure 1. Referring now to the drawings, the plate 10 includes a planar surface 12. A plurality of wells 18 are interspersed among the planar surface 12, and are arranged in rows and columns. Each well 18 includes a peripheral portion 20 and a concave wall 22 having a bottom 24, wherein the concave wall 22 is formed between peripheral portion 20 and bottom 24. The plate 10 also is provided with indicia 26 which may be in the form of numbers which indicate the specific wells for testing purposes. Surrounding the planar surface 12 is a trough 14 having walls 13a and 13b and a bottom 15. Trough 14 serves to collect samples which may have spilled out of well 18, thus protecting the work area and laboratory personnel. Surrounding trough 14 and extending distally therefrom is a flange 16, which aids one in handling and carrying the plate 10. In conducting an agglutination assay with the plate 10, the particles coated with a binder, a sample suspected of containing analyte, and any other additional reagents as needed, are placed into as many of the wells 18 as desired. The plate 10 then is rotated at a speed and for a period of time necessary to effect a proper agglutination reaction, if analyte is present. If analyte is present in the sample, a donut-shaped ring of agglutinated particles will form on the wall 22 of the well 18 after the rotation of plate 10. It also is to be noted that stirring of the reaction mixture in each well 18 is not required before rotation of the plate 10. The diameter to depth ratio of the wells 18, which may be from about 1.5:1 to about 11:1, preferably from about 5:1 to about 8:1, and more preferably from about 7:1 to about 7.5:1, enables one to effect a proper agglutination reaction without stirring, and enables the particles, upon rotation of the plate 10, to form a distinct donut-shaped ring pattern indicative of a positive test result. The invention now will be described with respect to the following example; however, the scope of the present invention is not intended to be limited thereby. EXAMPLE This example describes the use of an agglutination assay plate in accordance with the present invention having 24 wells arranged in four rows of six wells each. The plate is made of black high impact polystyrene having a matte finish. Each well is 11/16 inch wide and 3/32 inch deep. Blood is collected by venipuncture into a clean tube without anticoagulants and permitted to clot for 20 to 30 minutes at room temperature. The tube then is centrifuged at l,000xg for 10 to 15 minutes or until the supernatant is free of red blood cells. The serum then is transferred into a clean glass container. The plate is labeled to identify a high positive control row (wells 1-6), a low positive control row (wells 7- 12), and patient specimen rows (wells 13-18 and 19-24). The high positive control is a rubella virus antiserum containing buffer, human serum, stabilizer, and preservative (sodium azide, 0.1%). The low positive control contains the same materials as the high positive control, except that the low positive control has a lower titer of rubella virus. A negative control contains human serum, buffer, stabilizer, and preservative (sodium azide, 0.1%). The reagent latex includes latex particles sensitized with rubella virus, buffer, stabilizer, and preservative (sodium azide, 0.1%). A diluent contains buffer, stabilizer, and preservatives (sodium azide 0.1%). 20ul of the high positive control is added to well 1; 20ul of the low positive control is added to well 7; 20ul of patient serum is added to well 13; and 20ul of patient serum is added to well 19. 20ul of the negative control is added to well 12. 140ul of the diluent then is added to wells 1, 7, 12, 13, and 19, and 80ul of diluent is added to each of the remaining wells. The materials in wells 1, 7, 13, and 19 then are mixed slowly by drawing a micropipettor up and down five times. 80ul from each of wells 1, 7, 13, and 19 (i.e., the wells containing a 1:8 sample dilution) are transformed to the next well (wells 2,8, 14, and 20, respectively) and mixed. This 80 ul transfer then is repeated for wells 3 through 6, 9 through 11, 15 through 18, and 21 through 24. 80ul then is discarded from the last well in the series (wells 6, 11, 18, and 24) and from well 12. The reagent latex then is mixed thoroughly, and one drop of reagent latex is added to each well. The plate then is placed on a serologic slide shaker/rotator and rotated for 10 minutes at 95 to 105 rpm. After rotation, the agglutination patterns in each well are read under a high intensity incandescent lamp while holding the plate and rocking the plate gently back and forth. A positive result is indicated by a donut-shaped ring of agglutinated particles on the wall of the well. It is to be understood, however, that the scope of the present invention is not to be limited to the specific embodiments described above. The invention may be practiced other than as particularly described and still be within the scope of the accompanying claims.

Claims: What Is Claimed Is: 1. A plate for conducting agglutination assays comprising a planar surface and a plurality of wells in said planar surface, wherein each of said wells includes a circular peripheral portion and a concave wall having a bottom portion, wherein each of said wells has a diameter to depth ratio of from about 1.5:1 to about 11:1. 2. The plate of Claim 1 wherein said diameter to depth ratio is from about 5:1 to about 8:1. 3. The plate of Claim 2 wherein said diameter to depth ratio is from about 7:1 to about 7.5:1. 4. The device of Claim 1 and further comprising a trough surrounding said planar surface. 5. The device of Claim 4 and further comprising a flange extending distally from the periphery of said trough.

Inventors: SCHNEIDER HELEN, SCHRENK W JUERGEN, TABOLINSKY NICHOLAS, SCHNEIDER, HELEN, SCHRENK, W., JUERGEN, TABOLINSKY, NICHOLAS
Applicants: CARTER WALLACE, CARTER-WALLACE, INC.
Application year: 1994
Main classification: B01L3
IPC codes: B01L3